Combining thermopreference (T_p) and CO₂-gated heat-seeking assays, we studied the thermal preferendum and response to thermal cues in three Culex mosquito species exhibiting differences in native habitat and host preference (e.g., biting cold and/or warm-blooded animals). Results show that these species differ in both T_p and heat-seeking behavior. In particular, we found that Culex territans, which feed primarily on cold-blood hosts, did not respond to heat during heat-seeking assays, regardless of the CO₂ concentration, but exhibited an intermediate T_p during resting. In contrast, Cx. quinquefasciatus, which feeds on warm blooded hosts, sought the coolest locations on a thermal gradient and responded only moderately to thermal stimuli when paired with CO₂ at higher concentrations. The third species, Cx. tarsalis, which has been shown to feed on a wide range of hosts, responded to heat when paired with high CO₂ levels and exhibited a high T_p. This study provides the first insights into the role of heat and CO₂ in the host seeking behavior of three disease vectors in the Culex genus and highlights differences in preferred resting temperatures.

Insects are the most evolutionarily and ecologically successful group of living animals, being present in almost all possible mainland habitats; however, they are virtually absent in the ocean, which constitutes more than 99% of the Earth’s biosphere. Only a few insect species can be found in the sea but they remain at the surface, in salt marshes, estuaries, or shallow waters. Remarkably, a group of 13 species manages to endure long immersion periods in the open sea, as well as deep dives, i.e., seal lice. Sucking lice (Phthiraptera: Anoplura) are ectoparasites of mammals, living while attached to the hosts’ skin, into their fur, or among their hairs. Among them, the family Echinophthiriidae is peculiar because it infests amphibious hosts, such as pinnipeds and otters, who make deep dives and spend from weeks to months in the open sea. During the evolutionary transition of pinnipeds from land to the ocean, echinophthiriid lice had to manage the gradual change to an amphibian lifestyle along with their hosts, some of which may spend more than 80% of the time submerged and performing extreme dives, some beyond 2000 m under the surface. These obligate and permanent ectoparasites have adapted to cope with hypoxia, high salinity, low temperature, and, in particular, conditions of huge hydrostatic pressures. We will discuss some of these adaptations allowing seal lice to cope with their hosts’ amphibious habits and how they can help us understand why insects are so rare in the ocean.

Lice from pinnipeds, i.e. sea lions, seals, and walruses, are the only insects capable of surviving marine dives. Along their evolutionary history, they adapted to tolerate hypoxia, high salinity, low temperature and, in particular, to tolerate conditions of high hydrostatic pressure. To understand the limits of the capacity of lice to survive during host deep dives, we conducted a series of controlled experiments in the laboratory. We collected lice from elephant seals and submitted the different life stages to high pressure conditions. Lice were first exposed to one of four hydrostatic pressures: (a) 30 Kg/cm²; (b) 80 Kg/cm²; (c) 150 Kg/cm², or (d) 200 Kg/cm². They were then exposed a second time to higher or lower hydrostatic pressure conditions to test for the impact of the first experience, which could either be deleterious or trigger physiological adaption, allowing them a better tolerance to high pressure. We found that lice from elephant seals can tolerate hydrostatic pressures higher than 200 Kg/cm² (close to 200 atm), equivalent to 2000 m depth. Adults exhibited lower recovery times than nymphs after immersion at high hydrostatic pressure. Our findings show that lice developed unique adaptations to endure extreme marine conditions. We discuss these extreme performances as related to the morphological characteristics and physiological responses to diving in these insects.

The robber fly Mallophora ruficauda Weidemann (Diptera: Asilidae) is an important pest of apiculture in the Pampas of Argentina. As adults, they prey on honey bees and other insects, whereas the larvae are ectoparasitoids of Scarabaeidae grubs. Females of M. ruficauda lay eggs in grassland where the larvae drop to the ground after being wind‐dispersed and burrow underground searching for their hosts. A temporal asynchrony exists between the appearance of the parasitoid larvae and the host, with the parasitoid appearing earlier than the host. The present study investigates whether a strategy of synchronization with the host exists in M. ruficauda and determines which of the larval instars are responsible for it. Survival patterns and duration of the immature stages of the parasitoid are investigated to determine whether there is a modulation in the development at any time that could reduce the asynchrony. Experiments are carried out to determine the survival and duration of free‐living larval stadia in the absence of cues associated with the host. It is established that the first instar is capable of moulting to the second instar without feeding and in the absence of any cues related to the host, a unique event for parasitoids. Also, the first instar of M. ruficauda moults to the second stage within a narrow temporal window, and the second instar never moults in the absence of the host. After parasitizing a host, the second instar has the longest lifespan and is the most variable with respect to survival compared with the rest of the instars. All larval instars, except for those in the last (fifth) stadium, have a similar rate of mortality to that of second‐instar larvae. Additionally, it is established that the host is killed during the fourth (parasitoid) stadium and that the first‐ and fifth‐larval instars develop independently of the host. Finally, possible mechanisms that could aid in compensating for the asynchrony between the parasitoid and the host, promoting the host–parasitoid encounter, are discussed.